In the existing 3G (third generation) mobile communication network that connects calls of wireless terminals (UE: user equipment) such as mobile phones, even if a UE moves and a base station (wireless link logical node: Node B) to which the UE belongs changes to another base station, handover is performed to continue the telephone call.
With respect to the handover in the existing 3G network, the 3GPP standard (3rd Generation Partnership Project) has established various standards (for example, refer to Non-Patent Literature 1).
One related art reference discloses a system in which when a mobile terminal hands over between the existing 3G network and a wireless LAN, the mobile terminal can refer to GGSN (Gateway General Packet Radio Service Support Node) information at the handover destination coverage such that the mobile terminal can select the same GGSN as the handover source coverage (for example, refer to Patent Literature 1).
The applicant of the present patent application has disclosed a communication system that uses a femtocell base station (FAP: Femto Access Point) that connects a mobile terminal to a mobile communication core network through a wired channel of an IMS (IP Multimedia Subsystem) network installed at home, office, etc. (for example, refer to Patent Literature 2).
The communication system disclosed in Patent Literature 2 allows a mobile terminal that moves to continue a call by handover performed not only between FAPs, but also between the exiting 3G network that controls telephone calls using an MSC (Mobile Service Switching Center) and an FAP-based communication system that uses an IMS core network that controls calls.